This invention relates generally to the design and fabrication of inkjet printheads, and in particular to printheads configured to uniformly translate the position of printed ink drops on a receiver without altering the position of the printhead with respect to the receiver.
Traditionally, digitally controlled inkjet printing capability is accomplished by one of two technologies. The first technology, commonly referred to as xe2x80x9cdrop-on-demandxe2x80x9d, ejects ink drops from nozzles formed in a printhead only when an ink drop is desired to impinge on a receiver. The second technology, commonly referred to as xe2x80x9ccontinuousxe2x80x9d, ejects ink drops from nozzles formed in a printhead continuously with ink drops being captured by a gutter when ink drops are not desired to impinge on a receiver.
Referring to FIG. 1, a printhead 120, typically includes an approximately linear row of nozzles 122 which define printhead length 124 (measured in a direction along the nozzle row). Printhead 120 is scanned across a stationary receiver 126 in a fast scan direction 128. After fast scan 128 is complete, receiver 126 is moved in a receiver motion direction 130 relative to printhead 120. Typically, receiver motion 130 is orthogonal or substantially orthogonal to fast scan direction 128 and receiver 126 is moved in receiver motion 130 rather than displacing printhead 120 in a slow scan direction 132. Printhead 120 is subsequently scanned again in fast scan direction 128 with nozzles 122 having been physically displaced with respect to receiver 126 by an incremental amount (shown schematically so as to be easily compared to printhead length 124). The overall result is displacement of printhead 120 is in slow scan direction 132. Typically, displacement of printhead 120 with respect to receiver 126 in slow scan direction 132 is a fraction of nozzle to nozzle spacing 134. Typically, slow scan direction 132 is also orthogonal or substantially orthogonal to fast scan direction 128. Alternatively, printhead 120 can be physically stepped in slow scan direction 132 in order to physically displace printhead 120 with respect to receiver 126. Receiver 126 can also be moved in slow scan direction 132 in order to accomplish displacement of printhead 120 with respect to receiver 126. In either situation, either printhead 120 or receiver 126 is moved. Typically, the above-described motions are controlled by a controller 134. Many commercially available desktop printers (drop-on-demand printers, etc.) operate in this manner.
In continuous inkjet printers, receiver 126 is typically moved in fast scan direction 128 rather than printhead 120 because of the size and complexity of printhead 120. In many cases, printhead length 124 is pagewide and extends across the entire width of receiver 126 with fast scan direction 128 of receiver 126 being perpendicular to printhead length 124. This type of printhead and/or printer is commonly referred to as a xe2x80x9cpagewidthxe2x80x9d printhead/printer. Alternatively, printhead 120 can be scanned in fast scan direction 128, then stepped in slow scan direction 132 before printhead 120 scanned again in fast scan direction 128.
In some continuous printing applications, it is desirable to move printhead 120 in slow scan direction 132 in order to translate the pattern of printed ink drops (with respect to receiver 126) produced by nozzles 122. For example, in several conventional pagewidth printers, printhead 120 is translated or dithered a small distance from side to side in a direction parallel to its length (slow scan direction 132). This motion can be used to compensate for irregularities in nozzle to nozzle spacing 134 of printhead 120. Typical nozzle to nozzle spacing 134 is a multiple of the desired distance between printed dots. As such, printhead 120 can be displaced slightly along its length and fast scan 128 is repeated one or more times in order to print all desired dots. Typically, translated printed drop patterns are created by translating printhead 120 in slow scan direction 132 with respect to receiver 126. However, receiver 126 can be translated or displaced in slow scan direction 132 while printhead 120 remains stationary in slow scan direction 132.
Translation of the printhead in the slow scan direction is very precise. As such, commercially available mechanical devices that perform this task increase overall printer costs, are complex, and are prone to failure. Additionally, commercially available printheads often perform poorly when translated or dithered rapidly due to fluid acceleration along the length of the printhead. This is particularly true for pagewidth printheads because pagewidth printheads have extremely long fluid channels, typically distributed over the entire length of the printhead. Rapidly displacing the printhead intensifies the adverse affects of the fluid acceleration. As such, there is a need for an improved printhead translatable along its length (typically, in the slow scan direction relative to the receiver).
Additionally, it is advantageous to adjust the location of ink drop patterns printed on a receiver in the slow-scan direction in order to improve image quality. In this regard, displacing, dithering, or translating the printhead by an integral spacing relative to nozzle to nozzle spacing (the distance between nozzles) allows selected nozzles to print different data, thereby reducing image artifacts. The printhead motion (translation) needs to occur quickly in order to accomplish this. Typically, this motion is completed in a time much shorter in duration than the time required to scan in the fast scan direction. Again, currently available mechanical devices that accomplish this motion increase system cost and complexity. As such, there is a need for an improved printhead capable of adjusting the location of ink drop pattern printed on a receiver.
It is also advantageous to adjust the location of ink drop patterns printed on a receiver so as to slightly change the angle of the printhead relative to the fast scan direction in order to suppress image artifacts. This situation typically arises, for example, when the angle of the receiver changes while passing under the printhead. In many of these situations, changing the angle of the printhead relative to the fast scan direction needs to occur rapidly in order to prevent printed ink drops from misregistering (being printed on the wrong location) on the receiver. Again, currently available mechanical devices for moving the printhead at an angle relative to the fast scan direction add expense and complexity. Additionally, these devices can interfere with printhead performance during printhead motion in the fast scan direction due to the additional weight of the devices. As such, there is a need for an improved printhead capable of changing the angle of drops printed from a row of nozzles.
An object of the present invention is to provide an improved printhead translatable along its length.
Another object of the present invention is to provide an improved printhead rapidly translatable along its length that accurately and rapidly produces displaced printed drops in a direction parallel to the length of the printhead without interfering with the performance of the printhead.
Another object of the present invention is to provide an improved printhead capable of rapidly rotating the pattern of printed ink drops through an angle with respect to the receiver.
Yet another object of the present invention is to produce a displaced pattern of ink drops printed on a receiver without having to displace the receiver or the printhead.
Yet another object of the present invention is to provide an improved printhead having reduced cost and increased reliability.
According to a feature of the present invention, a continuous ink jet printing apparatus includes a nozzle array with portions of the nozzle array defining a length dimension. A drop forming mechanism is positioned relative to the nozzle array. The drop forming mechanism is operable in a first state to form ink drops having a first volume travelling along a path and in a second state to form ink drops having a second volume travelling along the path. A system applies force to the ink drops travelling along the path. The force is applied in a direction such that the ink drops having the first volume diverge from the path with the ink drops having the first volume being rotated relative to each other along the length dimension.
According to another feature of the present invention, a method of rotating ink drops ejected from a continuous ink jet printhead includes forming ink drops having a first volume travelling along a path; forming ink drops having a second volume travelling along the path; causing the ink drops having the first volume to diverge from the path; and causing the ink drops having the first volume to be rotated relative to each other.
According to another feature of the present invention, a method of translating ink drops includes forming a first ink drop travelling along a path; forming a second ink drop travelling along the path; causing the first ink drop to diverge from the path; and causing the second ink drop to diverge from the path rotated relative to the first ink drop.
According to another feature of the present invention, a continuous ink jet printing apparatus includes a nozzle array. A drop forming mechanism is positioned relative to the nozzle array. The drop forming mechanism is operable to form a first ink drop travelling along a path and a second ink drop travelling along the path. A system applies force to the first and second ink drops travelling along the path. The force is applied in a direction such that the first and second ink drops diverge from the path. At least a portion of the system is configured to reduce the force along the path such that the second ink drop is rotated relative to the first ink drop as the second ink drop diverges from the path.